Adsorption of polymer question

I'm trying to relate the concentration of moisture in an external environment with the concentration of moisture on the surface of a polymer. This is an adsorption and is it right to relate it using Henry's law? What is the explanation for this?

On a side note, what happens when moisture is adsorbed onto the surface of the polymer? Is it still a vapour or liquid?

I hope you can point me to some good sources or books that may be able to assist me in understanding this.